1. Field of Invention
The present invention generally relates to a method of fabricating an isolation structure. More particularly, the present invention generally relates to a method of fabricating a shallow trench isolation structure.
2. Description of Related Art
Following the advances in semiconductor technologies, the sizes of the semiconductor devices decrease down to the range of deep sub-microns. Isolation structures are now of great importance for isolating individual devices in high integration integrated circuits and inferior isolation structures may cause shorts between adjacent devices. At present, the most common isolation technology employs the shallow trench isolation (STI) structures.
FIG. 1 is a cross-sectional view for the process step of the typical STI process. Referring to FIG. 1, a substrate 100 with a patterned pad layer 102 and a patterned mask layer 104 formed thereon, and a shallow trench 110 formed therein, is provided. A liner oxide layer 120 is formed on the surface of the substrate within the shallow trench 110. After forming the liner oxide layer 120, an insulating oxide layer (not shown) is filled into the trench 110 and is densified. During the densification process, the high temperature may cause the liner oxide layer 120 to exert inconsistent compressive stress to the substrate 100, leading to dislocations occurring at corners of the substrate 100 under the trench 110.
Further, a silicon nitride layer 130 may be formed over the substrate 100 along the shallow trench 110, and the tensile stress generated by the silicon nitride layer 130 may compensate the compressive stress from the liner oxide layer 120 for relieving the dislocation.
However, top corners 135 of the shallow trench 110 often have corner thinning issues; that is, the liner oxide layer 120 at the top corners 135 is thinner than the other portions, which tends to cause the current leakage problem or the so-called kink effects.
For solving the above issues, photolithography and etching are performed to remove a portion of the silicon nitride layer 130 around the top corners of the shallow trench 110 using the patterned photoresist layer 140 as a mask. However, due to misalignment during the photolithography and etching process, the patterned photoresist layer 140 may cover too much or too less of the silicon nitride layer 130, as shown in FIG. 1, and the issue of corner thinning still remains.